Cite:
#develop (short for SharpDevelop) is a free IDE for C#, VB.NET and Boo projects on Microsoft\'s .NET platform. It is open-source, and you can download both sourcecode and executables from this site. In addition, you can find the latest information and changes on #develop, as well as get in touch with the team in the forum.
While,I just use this tiny IDE to research C#. quite useful!
really appreciate thinking of OPEN SOURCE.